<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 选择器 */
    .nnn{
        font-size: 40px;
        color: blue;
        background-color: aqua;
        text-align: center;
        line-height: 100px;
    }
    img{
        width: 400px;
        height: auto;
    }
    </style>
</head>
<body>
<h1 class="nnn">hello world</h1>
<img src="1.jpg" alt="啊嗷">
</body>
</html>